A membrane valve used more often in the area of refrigeration, and notably used in hermetic and/or semi-hermetic compressors which use an appropriate gas thus promoting the refrigeration effect is provided, allowing the above mentioned gas to be transferred from one chamber to the other, according to a pre-determined frequency as illustrated in FIGS. 1 and 2, when utilized in conjunction with a piston.
At the present moment, there exists an extensive variety of membrane valves, generally made of high carbon or stainless steel which, although presenting several manufacturing variations, have a common feature, a manufacturing process of stamping followed by tumbling, resulting, as illustrated in FIG. 9, in a monolithic structure, or a single part (A).
In a first manufacturing concept, a single part (A), generally made from a substantially thin metallic plate, a series of openings are produced, which externally define holes (B), with diverse functions, with at least one of such holes destined to the exhaust valve and the rest to the locking in place and assembly of the valve on the body of the head of a specific compressor and, internally defines, at least one cut or elongated opening (C1), which basically extends itself around the internal side of the body (A), defining at least one membrane (C), in FIG. 9, of any shape as in the tear-shaped example. Then, the body (A), which takes on the functions previously mentioned above, and at least one membrane, is subjected to an operation of rounding the corners by stamping, in-such a way as to avoid the concentration of tension points and the consequent formation of cracks upon operation.
As such, according to the first concept of the manufacturing process pertaining to the state of the method, the membrane valve is defined by at least one cut or elongated opening in a single part (A), in such a way that the membrane (C) continues to integrate the part (A) after punching, and thus presenting a series of disadvantages, as explained in the details to follow.
Generically, in regards to the dynamics of the operation, the membrane valves are comprised of an external section to be attached to the housing of the body of a compressor and at least one internal sections (membrane or reed) free to move (oscillate) in relation to the first sections and positioned over an area which is the intermediate point between the fluid entry duct and a suction chamber and which transfers such fluid to a chamber equally furnished with an exhaust valve. In this manner, at least one of the above mentioned central sections oscillates in accordance to the behavior of the said chamber and, in this condition, the exhaust valve is closed. In a following stage, where the fluid is compressed into the chamber, the membrane valve closes, while the exhaust valve is opened thus transferring the fluid to another duct, with the piston of a hermetic compressor providing the suction and transfer functions.
To satisfactorily execute the sequence of the operations described above, the membrane valves require certain manufacturing characteristics which, when present in larger numbers, are more adequate for its operation.
The first of such characteristics is the existence of the smallest possible radial gap (E) between each elongated opening and its respective membrane, basically around the central section of the body (A), in such a way that, from one side, it allows for freedom of movement of the membrane and, from the other side, little or no gas is retained around it, but is effectively transferred from one chamber to the other. Although the volume, which is usually filled by gas between the membrane and the rest of the body, is relatively small, considering that the body (A) is generally made of a substantially thin plate and, consequently, the quantity of gas stored within it is also a small amount, but, upon multiplying the same quantity of gas by the frequency of the typical operation of a medium size compressor of around 3,600 oscillations per minute, the quantity of the undesirably stored gas becomes considerable, causing a negative result on the efficiency of the assembly's operation, for the gas retained in it does not refrigerate. This situation becomes even more complicated in the case of semi-hermetic compressors, for in these, the oscillation of the reeds are considerably faster, mainly due to the fact that such type of compressor is widely used in several vehicles, in which the rotation is variable and may easily go over the 10,000 RPM range. In existing membrane valves, it is not always possible to obtain a reduced gap (E) between the membrane and the rest of the body for, according to its manufacturing process, it is necessary that a stamping (puncturing) tool be manufactured with reasonable resistance and thickness, which causes the production of a radial gap (E) of around at least 3 times the thickness of the plate.
Another desirable characteristic in this type of valve is the presence of comers which are softened or rounded at the edges of the body (A) and of the membrane (C) at the extension of the gap (E), in order to avoid tension accumulation due to frequent axial flexing of the membrane (C) during operation. Even if the radial gap (E) is somewhat elevated, as explained above, these edges do not present satisfactory softening after being tumbled in a barrel, for the abrasive necessary for the tumbling cannot satisfactory penetrate the gap (E), resulting in a less desirable finishing.
A third and last desirable aspect is the low cost of this type of valve, considering that it is part of a highly competitive market segment. It can be noticed from the operation described here, that the membrane (C) is the most frequently used part of the valve (A) and therefore, would need to be build out of a superior material, the opposite of the rest of the body (D); which acts solely as an assembly support and/or spacer and could be build of less expensive materials. However, considering that this manufacturing concept is based on the stamping of the valve into a single part, all of it should, therefore, be made of a superior, expensive material, even for the parts not subjected to great mechanical use.
In order to solve the above-mentioned problems the technical condition includes different processes, all of which were created so that the membrane valve is manufactured in two distinct parts, such as described in the Brazilian document PI 9.604.645-7 of Dec. 3, 1996, "PROCESS FOR THE MANUFACTURING OF A MEMBRANE VALVE FOR THE TRANSFERRING OF FLUIDS AND A MEMBRANE VALVE", with its construction, as per the illustration of FIG. 8, elaborated to handle different objectives, among which are highlighted:
1. the creation of a membrane valve in two distinct parts, one making up the body or part (D) and the other making up the reed (C) with both parts, however, kept together by an adhesive tape (F); PA1 2. the radial gap (E) between the corresponding edges of the two parts is substantially reduced to less than 3 times the thickness of the thin plate used in the body (D), and may be at least 0.05 mm, favoring the compressor's output, since the quantity of gas retained in the gap is insignificant; PA1 3. the increase of the service life of the puncturing tools used in the construction of the bodies (C) and (D), and especially the opening (C1), for punctures, which are more resistant than the ones on thin walls typical of the previous technique, may be used; PA1 4. reduction of the cost of valve manufacturing for it becomes possible to use expensive materials only in the main parts or reed (C); PA1 5. improves the service life of the valve in question, due to the increase of its wear resistance, created by the integral rounding of all the related corners, for the part (C) will have perfect corners for the abrasive may reach them adequately; PA1 6. increases the versatility of the process, allowing for investment reduction in raw material stocking and speeding up production, due to the versatility of the assembly obtained from standardizing one single body (D) which will receive different types of membranes (C), defined in accordance to the technical needs of each project; PA1 7. independently from the material used for the body and the reed, both are kept together (pre-assembled) by adhesive tape (F), applied in one of the faces of the assembly, where another tape should also be applied in order to balance the thickness of the first tape.
Although the technology described in the Brazilian document PI 9.604.645-7 has solved all the problems previously cited, it also generated another problem, related only to the pre-assembly between the body and the reed, for, as previously mentioned, the fixation of the two parts is made from using adhesive tapes, which will remain on the part permanently, that is, it will not be removed at the time of the final compressor assembly, and, therefore, cause some inconveniences, beginning with the presence of the actual tape; that is, although its thickness is very small, it considerably augments the thickness of the assembly, with the non standard part of such thickness concentrated in a certain area, and, therefore increasing the thickness of the total assembly and thus negatively interfering on the seal between the assembly components of the compressor's head. On the other hand, the adhesive tape is a product which includes different chemical components, where the more aggressive ones are used to form the adhesive part and, because of this, such chemical products will eventually damage parts of the actual compressor's head of the membrane, and may interfere in the operation, for instance by obstructing the capillary duct causing total failure of the compressor, for, as it was previously mentioned the reed (C) and the body (D) may be manufactured from different materials thus, by using the adhesive tape, it is necessary to have a rigorous quality control and testing for each material used, but still, the inconvenient increasing of thickness at a certain section persisted. Thus, for the manufacturing of the membrane valve, the ideal process would be manufacturing the valve from different materials, one for the reed and another for the body.
It would also be ideal for the two parts, reed and body, to be kept together. This condition has the purpose to speed up the process of the compressor's final assembly, eliminating the operations of selecting the reed and the body, as well as the alignment among both parts and in the assembly line. Although both parts are manufactured from different materials, they would be treated as a single part, this would speed up the final stage of the compressor's assembly. For this reason, the ideal condition would also be that the joining of the reed and the body be made without the use of additional material added to the assembly and without causing the increasing of the thickness. On the other hand, it would also be ideal for both parts, reed and body, to remain together and perfectly aligned and in the proper position for the final stage of the compressor's assembly.
In U.S. Pat. No. 5,140,748 of Aug. 25, 1992 "MANUFACTURING PROCESS OF A VALVE ASSEMBLY FOR A RECIPROCATING PISTON COMPRESSOR AND THE RESPECTIVE COMPRESSOR", there is a description of a certain technology to allow the adjustment between the reed and the body of the membrane valve. This adjustment, mainly, consists of providing mediums as shown in FIG. 10, so that the reed may be perfectly aligned to the opening corresponding to the valve's body. These mediums, in reality, become an integral part of the compressor's head and are presented in the form of 128 type pins, while the reed and the body will have in the adjacent edges 124-126 cuts which, combined amongst themselves, form or configure mediums to fit the said pins (128), and in such manner, finalizing the necessary resources for the correct alignment between the reed (C) and the valve's body (D). Logically, all these operations are performed at the time of assembly of the compressor's head. Such technical solution, as previously mentioned, will solve the alignment problem between the parts that form the membrane valve, but still, the selection of the two parts should be made at the assembly line, and it becomes extremely complicated when the said components are manufactured from different materials, and even more complicated when different membrane valves are used at the same assembly line. Hence, the technical solution proposed in U.S. Pat. No. 5,140,748 presents substantially high costs and the considerable complexity for manufacturing the assembly, for, besides positioning two items during the assembly, there is also the positioning pins which, in several occasions, cannot be fitted in the compressor's head.